Now that fall is around the corner, those of us fortunate enough to live in the Ohio Valley will soon be enjoying a show of brilliant fall color comparable to the legendary New England autumn display. If you’ve planned your garden for fall color, you can experience a rainbow effect right in your own yard. But what actually causes leaves to change from summer’s green to fall’s rainbow hues, and why do these colors seem different each year?
Fall color is caused by chemical reactions within plant leaves. There is actually a tug-of-war going on all year between chlorophyll (green) and various other pigments. During the growing season chlorophyll has the upper hand, but certain conditions will tip the balance in favor of other pigments.
Trees with strong yellow colors are influenced by the duration of sunlight. As the days grow shorter, chlorophyll starts to weaken and the yellow pigments dominate. At this point the tree is no longer producing and storing food, and is starting to go dormant. Yellow and orange pigments (carotenoids) take over and the leaves drop.
The red pigments that dominate certain plants are created as a response to environmental stresses such as light, dryness and temperature. Trees such as red maple, sweet gum, oakleaf hydrangea and Euonymus (‘burning bush”) use red pigments (anthocyanins) to protect the leaves under certain conditions. This makes the color vary quite a bit from year to year in both timing and intensity.
Trees that turn brown in fall (such as Oak) have high amounts of tannins, which help protect leaves from foraging animals and insects. Tannins take over from chlorophyll after the first frost, when the chlorophyll is “turned off” by the low temperature.
Since yellow pigments are always present in certain trees, fall color in the yellow range is the most consistent from year to year and varies mostly in the timing. The same is true of tannin-dominated trees, which always turn the same russet color.
Plants with red fall foliage are the most variable. They develop their most intense color after periods of cool, but not freezing, night temperature. The combination of bright sunny days and cool nights in fall, following a warm wet spring and mild summer drought, brings on the most stunning red fall displays.
You can orchestrate a spectacular show of fall color right in your own yard, by paying as much attention to fall foliage color as spring & summer bloom when choosing plants for your landscape. Take a good look around you as the season unfolds, and take notice of which plants really catch your eye. These are the plants to add to your landscape, your fall color “paint-box.” Fall is the best time to plant perennials and shrubs. A well-stocked nursery will have lots of choices right now to give your landscape “sizzle” for the rest of the season.
Steve Boehme is a landscape designer/installer specializing in landscape “makeovers”. “Let’s Grow” is published weekly; column archives are online at www.goodseedfarm.com. For more information call GoodSeed Farm Landscapes at (937) 587-7021.